undercooked bottom of cake what could be the reason?

I baked a cake and the bottom half of it for some reason is partially cooked and hard but the top is perfect and spongy, baked it as I usually do. Tried it again twice and the same thing happened. the oven seems to be working fine. never happened before, any idea what went wrong? in the picture you can see the undercooked side ontop as i turned it upside down before icing it thanks xx

Maybe you have the oven rack in the wrong place. I normally place my rack in the middle of the oven. Also, you may need to buy a small oven thermometer and once you heat the oven you need to check to see if your oven is cooking too hot. I hope you can figure out what your issue is. Good luck!!!